The field of this invention relates to the recovery of cesium from cesium-bearing minerals such as pollucite. More specifically, this invention relates to an improvement in such recovery processes wherein the cesium ore is extracted with sulfuric acid to obtain an extract containing cesium alum, CsAl(SO.sub.4).sub.2 for further processing.
Processes for the recovery of cesium from pollucite and other cesium-containing minerals were reviewed by J. J. Kennedy in Chemical Reviews, Vol. 23 (1938), pages 157-163. More recent technical developments were summarized by R. A. Heindl, Bureau of Mines Bulletin 650, "Mineral Facts and Problems" (1970 Ed.), pages 527-534.
In one process which has undergone considerable development for commercial use, ground pollucite ore is leached with strong sulfuric acid to obtain an extract containing cesium alum, which is recovered by crystallization. The cesium alum is redissolved in water at an elevated temperature, and reacted with an alkaline earth metal hydroxide, such as Ba(OH).sub.2 or Ca(OH).sub.2, to form an aluminum hydroxide precipitate together with precipitated BaSO.sub.4 or CaSO.sub.4. Cesium sulfate remains in the supernatant solution from which it can be recovered and converted into other cesium compounds. See Kirk-Othmer, Encylopedia of Chemical Technology, Vol. 5, page 331 (3rd ed., 1979); U.S. Pat. Nos. 3,112,169 and 3,207,751; and Chemical Reviews, cited above, page 161.
Cesium alum is cesium aluminum sulfate hydrate. Its formula can be expressed as CsAl(SO.sub.4).sub.2.x12H.sub.2 O, or as Cs.sub.2 SO.sub.4.Al.sub.2 (SO.sub.4).sub.3.24H.sub.2 O. The cesium alum as contained in the sulfuric acid extracts of pollucite is contaminated with other metal ions, such as rubidium, sodium, potassium, and iron. The crystallization of the cesium alum effects substantial purification, but the precipitate will contain at least trace amounts of other alums, such as rubidium alum, and other metal compounds such as iron sulfate. On redissolving the cesium alum precipitate, there is a need to separate not only the cesium from the aluminum but also from any other metal ions present as well as metal ions added in the precipitating agent.
While the cesium alum process is capable of producing cesium sulfate of relatively high purity, the process has proven to be difficult and expensive for commercial application. Therefore, there has been a recognized need for an improved process for recovering cesium from pollucite in a highly purified form. The need for such a process improvement has been emphasized in recent years by the increasing uses of cesium and cesium compounds, and by the projected expansion of these uses in anticipated applications. (See Heindl, above cited, pages 528-532.)